Respiratory protective device

ABSTRACT

A respiratory protective device is disclosed. The device is of a type which may be used in a noxious environment, such as a firefighting environment. The invention is characterized by a vented chamber of substantially fixed volume, two compliant breathing bags in the chamber, each having a filled volume in the chamber substantially equal to the chamber volume, a valving system to effect alternate normally prolonged use of the breathing bags, a source of oxygen-rich gas, and a scrubber to remove carbon dioxide from the gas. A unique scrubber apparatus is incorporated in preferred embodiments.

United States Patent Jansson 1 1 Dec. 2, 1975 1 RESPIRATORY PROTECTIVEDEVICE Primary ExaminerRichard A. Gaudet [76] Inventor: David GuildJansson, 85 Pond St., EmmmeFHemY Recla Natick, Mass. 01760 [22] Filed:July 29, 1974 ABSTRACT [21] Appl. No.: 492,740 A respiratory protectivedevice is disclosed. The device is of a type which may be used in anoxious environment, such as a firefighting environment. The in- 128/142123 1333 vention is characterized by a vented chamber of substantiallyfixed volume, two compliant breathing bags [58] Field of Search 128/142,142.2, 142.3,

128/145 5 145 6 145 7 145 8 188 202 203 in the chamber, each having afilled volume in the chamber substantially equal to the chamber volume,a valving system to effect alternate normally prolonged References cueduse of the breathing bags, a source of oxygen-rich gas, UNITED STATESPATENTS and a scrubber to remove carbon dioxide from the 2,711,1706/1955 Bernstein 128/203 gas. A unique scrubber apparatus isincorporated in 3021.8 2/1 2 preferred embodiments. 3,789,837 2/1974Philips et al. 128/1458 13 Claims, 3 Drawing Figures U.S. Patent 3 Dec;2, 1975 Sheet 1 of2 3,923,053

F IG.

inn-II- U.S. Patent Dec. 2, 1975 Sheet 2 Of2 3,923,053

RESPIRATORY PROTECTIVE DEVICE The invention described herein was made inthe performance of work under N.A.S.A Contract-No. NAS 12-2265 and issubject to the provisions of Section 305 of the National Aeronautics andSpace Act of 1958 (72 Stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION This invention relates to the field ofbreathing apparatus and particularly relates to respiratory protectivesystems such as are used by firefighters. This invention will bedescribed with particular referernce to systems usable by firefighters.However, it is to be understood that this invention is applicable toother fields, such as where protection from noxious environments isnecessary. The description in terms of firefighters equipment andproblems is merely for purposes of convenience.

In. recent years, more and more people have become awareof the dangersinvolved in firefighting and of the need for improvement in the area ofprotection for firefighters There is increasing interest in research anddevelopment in areas such as the identification of the environment towhich the firefighter is exposed, new and improved methods and equipmentfor firefighting, and new safety and protection equipment for thefirefighter.

According to a recent set of statistics, firefighting can be called oneof the most dangerous occupations. Firemen are exposed to stresses ofmany kinds including extreme temperature conditions (both heat andcold), physical stresses caused by the difficult working environment ofa fire, emotional stresses of being in a dangerous environment, andadditional environmental stresses caused by particulate, gaseous, andvapor combustion products.

There are two significant constituents of the combustion atmospherewhich are known to justify the need for respiratory protection. Thepresence of elevated levels of carbon monoxide in the fire environmentis a constant hazard to firemen. Carbon monoxide is dangerous because ofthe following property. Hemoglobin, the compound in blood which absorbsoxygen for use throughout the body, combines with carbon monoxide toform carboxyhemoglobin, thereby keeping that hemoglobin from combiningwith oxygen. The affinity of hemoglobin for carbon monoxide is 200 300times that of its affinity for oxygen. For example, a typical one literbreath of air contains 800 milliliters of nitrogen and 200 millilitersof oxygen. In the course of its stay in the lungs, about milliliters ofoxygen are absorbed and some carbon dioxide is added. However, if thatliter of air had contained only one milliliter of carbon monoxide(0.1%), this small amount of carbon monoxide could effectively keep agood part of the necesary oxygen from being absorbed during that breath.It is, therefore, easy to understand why carbon monoxide is such adangerous contaminant.

The second important characteristic of the combustion atmosphere is itsdepressed level of oxygen. Large amounts of oxygen are consumed in afire, thereby creating a shortage of oxygen for breathing. Normal aircontains approximately 20% oxygen and about 16% is considered to be aminimum level of oxygen acceptable for respiration. Consequently, evenif all noxious contaminants in the fire atmosphere could be filteredand- 2 /or absorbed from the air before breathing, such air would notcontain an adequate concentration of oxygen. Therefore, the firefightermust carry some type of oxygen supply with him into a fire.

In the prior art, there are two basic types of respirator systems foruse by firefighters. One is a compressed air system and the other is anoxygen rebreather system.

A compressed air system consists of a large compressed air tank with ademand regulator which provides air to a mask during inhalation. The twomajor problems of this type of system are excessive total weight andshort operating time.

An oxygen rebreather system includes a significantly smaller tankcontaining pure oxygen in the gaseous or liquid state. The remainder ofthe system consists of a breathing bag, a chemical scrubber for removingcar-- bon dioxide, and a mask for delivering oxygen to the user.Initially, the breathing bag is filled and the wearer inhales directlyfrom the breathing bag and exhales through the carbon dioxide scrubberback into the breathing bag. The only nitrogen in the system is thatwhich is present initially, and this is soon lost through a safety valveon the bag which prevents the bag from inflating as the oxygen is slowlyleaked into it. Thus the concentration of oxygen in the mask isapproximately throughout most of the operating time. There are severalproblems with this system. The most significant of these is the safetyhazard caused by having almost pure oxygen in the space around the mansface, especially if the mask is accidentally knocked out of position ina fire. Furthermore, for very prolonged use, pure or very high oxygenconcentration in inhaled gas is physiologically dangerous to man. Otherproblems include the impedance to breathing and the high temperature ofthe inhaled gas caused by the chemical reactions of the scrubbermaterial.

BRIEF SUMMARY OF THE INVENTION The new respirator system provides alightweight, longer-lasting respiratory protective system which, at thesame time, provides the firefighter with gas containing a safer level ofoxygen, when compared with present compressed air and rebreathersystems. Furthermore, the novel scrubber provides cooler operation thantypical oxygen rebreather scrubbers.

The respiratory protective device of my invention includes a chamber ofsubstantially fixed volume and two alternatively active compliantbreathing bags contained therein, each having a volume substantiallyequal to the chamber volume. The respirator of my invention has a sourceof oxygen-rich gas and a valving system to effect alternate, normallyprolonged, use of the breathing bags. A scrubber is used to removecarbon dioxide from the exhaled air. A preferred embodiment includes ascrubber, described hereinafter, which delivers cool gas to the user.The scrubber is situated in a breathing conduit loop which, at any time,also includes the active breathing bag therein. Such conduit loop formsa means to deliver gas from the system to the user, such as a mask or amouthpiece and one or more lengths of flexible hose.

The system embraces the idea of rebreathing oxygenrich gas from abreathing bag until the gas has a con centration of oxygen low enough tonecessitate discarding the gas. This old gas is then vented to theatmosphere, and a fresh volume of gas is supplied. Each breath lowersthe concentration of oxygen until a lower limit is reached. Two similar,compliant bags are used.

While the active bag is being filled the inactive bag is vented. Thesesimultaneous filling and venting operations can be done conveniently byconstraining the volume of the two bags in a single, stiff, ventedenclosure the size of one bag. The expansion of the bag being filledcontracts the inactive bag to push the old gas through a passive valveto the atmosphere. The volume of fresh gas is preferably less than theconstraining volume of the enclosure (often referred to herein as achamber"), thus partially venting the inactive bag to the atmosphere.The advantage of this partial filling is that the peak concentration ofoxygen in gas being breathed may be lower than the concentration ofoxygen in the oxygen-rich supply source.

The unique scrubber apparatus disclosed provides cooler system operationand lower impedance to breathing than the prior art. Molecular sievematerial is used to remove the carbon dioxide from the exhaled gas sincethis material produces significantly lower heat than the commonly usedmaterial, soda lime. Both soda lime and the molecular sieve materialalso remove water and, in doing so, produce a considerable amount ofheat. Therefore, a desiccant, such as CaSO, is used upstream of themolecular sieve material to remove the water with very much less heatgenerated, providing a scrubber with considerably cooler operation thantypical rebreather scrubbers today. In addition, large crosssectionalarea and lower depth of material keep flow velocity in the scrubber low,thus lowering the breathing impedance of the scrubber.

The advantages of this respiratory protective device are that itprovides a lightweight, longer-lasting, and more compact system than asimple compressed air device and provides safer and cooler operationthan a pure oxygen rebreather.

A primary object of this invention, therefore, is to provide a systemwhich overcomes the aforementioned problems.

Another object of this invention is to provide a lightweight, compactrespirator.

Another object of this invention is to provide a respi rator which canbe used for longer periods of time without replenishment of the supplyof breathing gas.

Still another object of this invention is to provide a respirator whichoperates at a safe level of oxygen concentration.

A further object of this invention is to provide a respiratoryprotective device which operates at a cool temperature with a minimum ofbreathing effort.

These and other important objects of the invention will become apparentfrom the following description and drawings showing preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional schematic ofthe respiratory protective device which will be used to describe thedesign and operation of the new system.

FIG. 2 is an enlarged sectional view of the scrubber used in theembodiment of FIG. 1 taken along section 2-2 as shown in FIG. 1.

FIG. 3 is a perspective view illustrating the compactness of a preferredembodiment of this invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Throughout the figures,like numerals are used for identification of like elements and parts.

A preferred embodiment of this invention is illustrated by the schematicdrawing of FIG. 1. The respirator of FIG. 1 includes a vented bagchamber 10 having a substantially fixed volume. The chamber has wallsthrough which the surrounding atmosphere can pass freely. An example ofthe type of material out of which the walls are made is common windowscreen. However, any material having sufficient strength and enoughholes over a major portion of the chamber to allow free passage of thesurrounding atmosphere is suitable for construction of chamber 10. Bagchamber 10 houses breathing bags 12 and 14. The volume of the bags 12and 14 is constrained by the chamber 10 so that when either bag is full,its volume is substantially equal to the volume of chamber 10.Substantially equal" does not necessarily imply close to of chambervolume, though this is preferred The term, however, does imply enoughfilled volume for bag interaction. Breathing bags 12 and 14 areextremely compliant, meaning that adding gas to increase the volume ofthe bags does not increase the pressure of the gas in the bags.(Mathematically, (dP/dV) is equal to or very close to zero, where (dP/dV) is the derivative of the gas pressure in the bag with respect to thevolume'of the bag). Examples of materials that can be used for breathingbags are neoprene sheeting and common polyethylene sheeting. Othersuitable materials will be obvious to those skilled in the art to whomthis invention has been disclosed. Therefore, chamber 10 constrains bags12 and 14 in a way such that if bag 12 is filled with gas, the fillingprocess will force the gas in bag 14 to be expelled, and vice versa.Bags 12 and 14 are connected to tank 24, which contains a compressedsupply of oxygen-rich gas, through valve means 22, valve 20, andconstant pressure regulator 26. Valve means 22 can be switched into twomodes, either connecting bag 12 to valve 20 or connecting bag 14 tovalve 20. Valve 20 is open for a short period of time to allow gas fromtank 24 through regulator 26 to fill one of the breathing bags. Controlof valve means 22 and valve 20 is accomplished by a controller 40. Valvemeans 22, valve 20, and the control means form a means to open thesource of breathing gas (tank 24) to alternately fill bags 12 and 14with a quantity of breathing gas. The detailed description of thefunction of controller 40 will be given hereinafter. The respirator ofFIG. 1 further includes a breathing conduit loop having a breathingconduit 30, an inhalation check valve 32, a mask 28 for delivery of thegas to the user, an exhalation check valve 34, a breathing conduit 36, achemical scrubber 38, and a valve means 16 to which both bags areconnected. Valve means 16 can be switched into two modes, eitherconnecting bag 12 into the breathing conduit loop and bag 14 to theatmosphere through a check valve 18 or connecting bag 14 into thebreathing conduit loop and bag 12 to the atmosphere through check valve18. Valve means 16, check valve 18, and the control means form a meansto alternately vent bags 12 and 14 as the activated bag is being filled.Means for delivery of the gas to the user can also be a mouthpiece,complete helmet, or other suitable device in place of mask 28.Therefore, the breathing gas is fed to and from mask 28 from either bag12 or bag 14 by the breathing conduit loop. Valve means 16 is alsocontrolled by controller 40, described hereinafter. Valve means 16 andthe control means form a means to alternately activate bags 12 and 14for breathing.

The control means in this particular embodiment of the respirator ofFIG. 1 contains a battery power supply and electronic circuitry incontroller 40 and microswitches located in valve means 16 and 22.Details of a suitable control means will be obvious to a man skilled inthe art to whom this invention has been disclosed. A wide variety ofcontrol means, including various types of apparatus, are suitable foruse in this invention and such would be obvious. The control means alsoincludes a means of determining the oxygen concentration in thebreathing conduit loop, that is a means to determine when theconcentration of oxygen is at a predetermined lowest tolerable level.This function can be done by several methods, some of which are asfollows: a direct measurement of oxygen concentration using an oxygensensor, a flow integrator to measure the total volume of inhaled gas andinfer the oxygen concentration, approximate flow integration schemes toinfer volume and thus oxygen concentration, or a timer from which anestimate of the oxygen concentration can be made. Several approximateflow integration schemes are possible, the simplest example of which isa breath counter. The reason for determining the oxygen concentration inthe breathing conduit loop will be explained in the detailed descriptionof the respirator system operation which follows. Methods and means todetermine (measure or approximate) the oxygen concentration of the gasin the breathing conduit loop would be obvious to someone skilled in theart to which this invention has been disclosed.

FIG. 2 is an enlarged sectional view of the scrubber 38 of FIG. 1illustrating a unique scrubber used in preferred embodiments of thisinvention. Scrubber 38 includes an airtight case 100, inlet port 102,outlet port 104, chemical material layers including an upstream scrubbermaterial layer 106 and a downstream scrubber material layer 108, screens110, 112 and 114, separating and/or isolating layers 106 and 108 anddefining, with case 100, plenum chambers 116 and 118. Exhaled gascontaining oxygen, carbon dioxide, water, and other gaseous componentssuch as nitrogen, passes into the plenum chamber 116 through inletport102 in the direction indicated by the arrows. The first or upstreamlayer 106 is an efficient desiccant having a low K cal of desiccation,which removes water from the exhaled gas. A highly preferred suchdesiccant material is CaSO commercially known as Drierite. The heat ofdesiccation of CaSO, is 2.7 cal per mole of H 0, compared with about 40k cal per mole of H for the commonly used scrubber material, soda lime.Low heat of desiccation refers to a heat of desiccation substantiallyless than that of soda lime, normally no more than 20 k cal per mole ofH 0, and preferably much less. Other acceptable desiccant materialsmeeting the above criteria would be obvious to those skilled in the artand aware of this invention. The second or downstream layerl08 ismolecular sieve material such as Union Carbide molecular sieve A (Ca-,Na [(AlO 30 B 0) which adsorbs both water and carbon dioxide, and hasa low heat of carbon dioxide adsorption, about half of that of sodalime. The heat produced by the hydration of CaSO, is significantly lessthan that produced by the adsorption of water by the molecular sievematerial. Thus, the total amount of heat produced by this new scrubberkeeps the gas in the respirator significantly cooler than if existingscrubbers of the wellknown type using soda lime were used. The largecrosssectional area of the scrubber provides a lower pressure dropacross the scrubber for a given flow rate so that the breathingimpedance of the respirator is low. The exhaled gas passes from plenum116 through screens 110, 112, 114 and layers 106 and 108, into plenum118 and out through port 104..

A typical cycle of operation of the respirator of FIG. 1 is as follows.For this description, the breath counting scheme will be used toestimate the oxygen concentration of the gas in the breathing conduitloop. The activated bag 12 contains oxygen-rich gas just after beingfilled. Bag 12 is, therefore, connected by valve means 16 to mask 28 bythe breathing conduit loop. Valve means 16, while placing the activatedbag 12 in the breathing conduit loop, also connects the deactivated bag14 to the surrounding atmosphere through check valve 18 which allows gasto pass only from the deactivated bag 14 to the atmosphere. The user,wearing mask 28, inhales gas from bag 12 and exhales gas throughscrubber 38 back into bag 12. The concentration of oxygen in bag 12 islowered with each breath. Scrubber 38 chemically removes the carbondioxide and water from the exhaled gas. The breath counter in controller40 counts the number of breaths that the user has breathed from the bag12 and when a predetermined number has been reached, controller 40begins the switching sequence, which deactivates bag 12, activates bag14, fills bag 14, and allows venting of bag 12 through check valve 18.When the controller 40 starts the switching sequence, valve means 16places bag 14 into the breathing conduit loop and connects bag 12 to theatmosphere through check valve 18. Thus bag 12 and bag 14 have switchedroles, bag 14 now being the activated bag and bag 12 the deactivatedbag. Since the end of the previous switching sequence, valve 22 has beenin a mode connecting valve 20 to bag 14. Immediately after the change ofvalve means 16, the controller 40 activates valve 20 for a preset shortinterval of time to allow a supply of oxygen-rich gas to pass from tank24 through regulator 26, valve 20, and valve 22 into thenewly-activatedbag 14. The filling of bag 14 causes the expansion of bag14 in the chamber 10, thus causing the contraction of bag 12 in thechamber 10 by the physical interaction of bags 12 and 14, expelling thegas in bag 12 through check valve 18 to the atmosphere. If the volume ofthe newly-filled activated bag 14 is less than the volume of the chamber10, then some of the gas in bag 12 will remain to be used after the nextswitching sequence which will activate bag 12 and deactivate bag 14.When the controller 40 closes valve 20, controller 40 then activatesvalve 22 which changes to the mode connecting valve 20 to bag 12, readyfor the next switching sequence. The user now breathes from theactivated bag 14 in the breathing conduit loop and the breath countercounts the number of breaths from bag 14. The oxygen concentration ofthe gas in bag 14 decreases with each breath until the breath counterreaches the predetermined number, at which point the switching sequenceis begun by controller 40. This switching sequence reverses the roles ofbag 12 and bag 14 again, filling the newly-activated bag 12 andexpelling gas from bag 14 in the same manner as the switching sequencedescribed above. Similarly, valve 22 now switches to a mode connectingbag 14 to valve 20 for filling of bag 14 during the next switchingsequence. The respirator continues to operate through repetitive cyclesduring the entire period of use, thus making very efficient use of theoxygen contained in supply source 24, while keeping a low oxygen concen-7 tration in the gas breathed from the breathing conduit loop.

FIG. 3 shows a preferred arrangement of the components of the respiratoron a backpack base 130. Scrubber 38 is the device shown in FIG. 2. Valvemeans 16 and 22, valve 20, and check valve 18 are shown contained in asingle valve package 134 with controller 40 placed next to valve package134 for ease of wiring. Bag chamber 10 is mounted to valve package 134so that bags 12 and 14, not visible in FIG. 3, can easily be connectedto valve means 16 and 22. Tank 24 and regulator 26 are mounted on thebottom of the base 130. Conduits 30 and 36 connect the system to themask 28 (not shown) with check valves 32 and 34 (also not shown) mountedin the mask 28. High pressure conduit 42, shown also in FIG. 1, connectsregulator 26 to valve in valve package 134. The components of therespirator of this invention may be placed in a compact, lowprofilearrangement which is easily worn by a firefighter. The compactarrangement of the respirator of FIG. 3 may be worn easily by a man,either on his back or on his chest, or elsewhere. Other compact ordistributed arrangements of the components of the respirator of thisinvention would be obvious to thos skilled in the art to whom thisinvention has been disclosed.

Various materials useful in the components of embodiments of thisinvention will be apparent to those skilled in the art to whom thisinvention has been disclosed.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments, and many details have beenset forth for purpose of illustration, it will be apparent to thoseskilled in the art that the invention is susceptible to additionalembodiments and that certain of the details described herein can bevaried considerably without departing from the spirit of the invention.

I claim:

1. A respirator comprising;

a source of oxygen-rich gas;

a chamber having a substantially fixed volume, said chamber beingvented;

first and second compliant breathing bags within said chamber, each ofsaid bags having a filled volume within said chamber substantially equalto the volume of the chamber;

means to alternately activate one of said bags for breathing;

means to open said source to fill said activated bag with a quantity ofsaid gas; and

means to vent the other bag as said activated bag is filled, said otherbag being contracted by expansion of said activated bag during filling.

2. The respirator of claim 1 further having a breathing conduit loop,said means to activate connecting said activated bag into said loop,said loop including a scrubber to remove carbon dioxide from exhaledgas.

3. The respirator of claim 2 wherein said scrubber comprises separateupstream and downstream chemi- 8 cal scrubber materials within saidloop, said upstream scrubber material being an efficient desiccanthaving a low heat of desiccation and said downstream scrubber materialbeing a molecular sieve which is adsorbent of carbon dioxide and havinga low heat of adsorption, whereby scrubbed gas is not substantiallyheated.

4. The respirator of claim 1 wherein said quantity of said gas from saidsource filled into said activated bag is less than said filled volume.

5. The respirator of claim 2 wherein said quantity of said gas from saidsource filled into said activated bag is less than said filled volume.

6. The respirator of claim 1 wherein said means to activate includesmeans to determine when the concentration of oxygen is at a lowesttolerable level.

7. The respirator of claim 2 wherein said means to activate includesmeans to determine when the concentration of oxygen is at a lowesttolerable level.

8. In breathing apparatus of the type having a supply source ofbreathable gas and breathing bag means replenished by said source, theimprovement comprising:

a chamber having a substantially fixed volume, said chamber beingvented; first and second alternately active compliant breathing bagswithin said chamber, each of said bags having a filled volume ofsufficient extent within said chamber such that the filling of one bagcauses physical interaction thereof with the other bag whereby saidother bag is at least partially deflated;

means to alternately activate one of said bags for breathing, the otherof said bags to be inactive until thereafter activated; and

means to determine when to switch bags.

9. The improvement of claim 8 wherein said supply source comprises asource of oxygen-rich gas.

10. The improvement of claim 9 further including means to open saidsource to fill said activated bag with a quantity of said gas, saidquantity being less than said filled volume.

11. The improvement of claim 9 further having a breathing conduit loop,said first and second breathing bags being alternately connected intosaid loop, said loop including a scrubber to remove carbon dioxide fromexhaled gas.

12. The improvement of claim 11 wherein said scrubber comprises separateupstream and downstream chemical scrubber materials within said loop,said upstream scrubber material being an efficient desiccant having alow heat of desiccation and said downstream scrubber material being amolecular sieve which is adsorbent of carbon dioxide and having a lowheat of adsorption, whereby scrubbed gas is not substantially heated.

13. The improvement of claim 12 further including means to open saidsource to fill said activated bag with a quantity of said gas, saidquantity being less than said filled volume.

1. A respirator comprising: a source of oxygen-rich gas; a chamberhaving a substantially fixed volume, said chamber being vented; firstand second compliant breathing bags within said chamber, each of saidbags having a filled volume within said chamber substantially equal tothe volume of the chamber; means to alternately activate one of saidbags for breathing; means to open said source to fill said activated bagwith a quantity of said gas; and means to vent the other bag as saidactivated bag is filled, said other bag being contracted by expansion ofsaid activated bag during filling.
 2. The respirator of claim 1 furtherhaving a breathing conduit loop, said means to activate connecting saidactivated bag into said loop, said loop including a scrubber to removecarbon dioxide from exhaled gas.
 3. The respirator of claim 2 whereinsaid scrubber comprises separate upstream and downstream chemicalscrubber materials within said loop, said upstream scrubber materialbeing an efficient desiccant having a low heat of desiccation and saiddownstream scrubber material being a molecular sieve which is adsorbentof carbon dioxide and having a low heat of adsorption, whereby scrubbedgas is not substantially heated.
 4. The respirator of claim 1 whereinsaid quantity of said gas from said source filled into said activatedbag is less than said filled volume.
 5. The respirator of claim 2wherein said quantity of said gas from said source filled into saidactivated bag is less than said filled volume.
 6. The respirator ofclaim 1 wherein said means to activate includes means to determine whenthe concentration of oxygen is at a lowest tolerable level.
 7. Therespirator of claim 2 wherein said means to activate includes means todetermine when the concentration of oxygen is at a lowest tolerablelevel.
 8. In breathing apparatus of the type having a supply source ofbreathable gas and breathing bag means replenished by said source, theimprovement comprising: a chamber having a substantially fixed volume,said chamber being vented; first and second alternately active compliantbreathing bags within said chamber, each of said bags having a filledvolume of sufficient extent within said chamber such that the filling ofone bag causes physical interaction thereof with the other bag wherebysaid other bag is at least partially deflated; means to alternatelyactivate one of said bags for breathing, the other of said bags to beinactive until thereafter activated; and means to determine when toswitch bags.
 9. The improvement of claim 8 wherein said supply sourcecomprises a source of oxygen-rich gas.
 10. The improvement of claim 9further including means to open said source to fill said activated bagwith a quantity of said gas, said quantity being less than said filledvolume.
 11. The improvement of claim 9 further having a breathingconduit loop, said first and second breathing bags being alternatelyconnected into said loop, said loop including a scrubber to removecarbon dioxide from exhaled gas.
 12. The improvement of claim 11 whereinsaid scrubber comprises separate upstream and downstream chemicalscrubber materials within said loop, said upstream scrubber materialbeing an efficient desiccant having a low heat of desiccation and saiddownstream scrubber material being a molecular sieve which is adsorbentof carbon dioxide and having a low heat of adsorption, whereby scrubbedgas is not substantially heated.
 13. The improvement of claim 12 furtherincluding means to open said source to fill said activated bag with aquantity of said gas, said quantity being less than said filled volume.